Method and apparatus for transmitting receipt acknowledgement in wireless communication system

ABSTRACT

One embodiment of the present invention relates to a method for a second user equipment transmitting a receipt acknowledgement in a wireless communication system, the method for transmitting the receipt acknowledgement comprising the steps of: the second UE receiving data from the first UE; determining a subframe to transmit the receipt acknowledgement by comparing a time resource pattern for transmission (T-RPT) of the first UE and a T-RPT of the second UE; and transmitting the receipt acknowledgement relating to the data from the determined subframe to the first UE.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/077,880, filed on Aug. 14, 2018, now allowed, which is a NationalStage application under 35 U.S.C. § 371 of International Application No.PCT/KR2017/001595, filed on Feb. 14, 2017, which claims the benefit ofU.S. Application No. 62/295,141, filed on Feb. 14, 2016. The disclosuresof the prior applications are incorporated by reference in theirentirety.

TECHNICAL FIELD

Following description relates to a wireless communication system, andmore particularly, to a method of transmitting ACKnowledgment/NegativeACKnowledgment (ACK/NACK) and an apparatus therefor.

BACKGROUND ART

Wireless communication systems have been widely deployed to providevarious types of communication services such as voice or data. Ingeneral, a wireless communication system is a multiple access systemthat supports communication of multiple users by sharing availablesystem resources (a bandwidth, transmission power, etc.) among them. Forexample, multiple access systems include a Code Division Multiple Access(CDMA) system, a Frequency Division Multiple Access (FDMA) system, aTime Division Multiple Access (TDMA) system, an Orthogonal FrequencyDivision Multiple Access (OFDMA) system, a Single Carrier FrequencyDivision Multiple Access (SC-FDMA) system, and a Multi-Carrier FrequencyDivision Multiple Access (MC-FDMA) system.

D2D communication is a communication scheme in which a direct link isestablished between User Equipments (UEs) and the UEs exchange voice anddata directly without an evolved Node B (eNB). D2D communication maycover UE-to-UE communication and peer-to-peer communication. Inaddition, D2D communication may be applied to Machine-to-Machine (M2M)communication and Machine Type Communication (MTC).

D2D communication is under consideration as a solution to the overheadof an eNB caused by rapidly increasing data traffic. For example, sincedevices exchange data directly with each other without an eNB by D2Dcommunication, compared to legacy wireless communication, networkoverhead may be reduced. Further, it is expected that the introductionof D2D communication will reduce procedures of an eNB, reduce the powerconsumption of devices participating in D2D communication, increase datatransmission rates, increase the accommodation capability of a network,distribute load, and extend cell coverage.

Currently, discussion on V2X communication associated with D2Dcommunication is in progress. The V2X communication corresponds to aconcept including V2V communication performed between vehicle UEs, V2Pcommunication performed between a vehicle and a UE of a different type,and V2I communication performed between a vehicle and an RSU (roadsideunit).

SUMMARY

A technical task of the present invention is to provide a method for auser equipment to transmit ACK/NACK in D2D, V2X communication and thelike.

Technical tasks obtainable from the present invention are non-limited bythe abovementioned technical task. And, other unmentioned technicaltasks can be clearly understood from the following description by thosehaving ordinary skill in the technical field to which the presentinvention pertains.

To achieve these and other advantages and in accordance with the purposeof the present invention, as embodied and broadly described, accordingto one embodiment, a method of transmitting ACK/NACK(ACKnowledgment/Negative ACKnowledgment), which is transmitted by asecond UE (User Equipment) in a wireless communication system, includesthe steps of receiving data, by the second UE, from a first UE,determining a subframe in which ACK/NACK is to be transmitted bycomparing T-RPT (Time Resource Pattern for Transmission) of the first UEwith T-RPT of the second UE, and transmitting ACK/NACK to the first UEin the determined subframe in response to the data.

To further achieve these and other advantages and in accordance with thepurpose of the present invention, according to a different embodiment, asecond UE (User Equipment) transmitting ACK/NACK(ACKnowledgment/Negative ACKnowledgment) in a wireless communicationsystem includes a transmitter and a receiver, and a processor, theprocessor configured to control the receiver to receive data from afirst UE, the processor configured to determine a subframe in whichACK/NACK is to be transmitted by comparing T-RPT (Time Resource Patternfor Transmission) of the first UE with T-RPT of the second UE, theprocessor configured to control the transmitter to transmit ACK/NACK tothe first UE in the determined subframe in response to the data.

The comparison between the T-RPT of the first UE and the T-RPT of thesecond UE can be performed on subframes appearing after a k^(th)subframe from a subframe in which the data is received.

The second UE can determine a first subframe of which a T-RPT value ofthe first UE corresponds to 0 and a T-RPT value of the second UEcorresponds to 1 as the subframe in which the ACK/NACK is to betransmitted among the subframes appearing after the k^(th) subframe.

The second UE can repeatedly transmit the ACK/NACK in a number ofsubframes of which the T-RPT value of the second UE corresponds to 1appearing after the first subframe.

The second UE can repeatedly transmit the ACK/NACK in a number ofsubframes of which the T-RPT value of the first UE corresponds to 0 andthe T-RPT value of the second UE corresponds to 1 appearing after thefirst subframe.

ACK/NACK can be transmitted together in the a number of subframes inresponse to data other than the data.

The T-RPT of the first UE and the T-RPT of the second UE can bedetermined by the first UE and the second UE, respectively.

The T-RPT of the second UE may correspond to T-RPT circularly shiftedfrom the T-RPT of the first UE as much as a predetermined value.

The first UE corresponds to a relay UE and the second UE may correspondto an MTC (Machine Type Communication) UE.

The number of 1s included in the T-RPT of the second UE can be includedin a predetermined range.

The subframe in which the ACK/NACK is to be transmitted can include mostrecently received control information prior to the subframe or channelstate information on data.

The k may correspond to 4.

According to the present invention, when ACK/NACK is transmitted incommunication rather than cellular communication, it is able to solve aproblem due to a half-duplex constraint.

Effects obtainable from the present invention are non-limited by theabove mentioned effect. And, other unmentioned effects can be clearlyunderstood from the following description by those having ordinary skillin the technical field to which the present invention pertains.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this specification, illustrate embodiments of the invention andtogether with the description serve to explain the principles of theinvention.

FIGS. 1A and 1B are diagrams for a structure of a radio frame;

FIG. 2 is a diagram for a resource grid in a downlink slot;

FIG. 3 is a diagram for a structure of a downlink subframe;

FIG. 4 is a diagram for a structure of an uplink subframe;

FIGS. 5A and 5B are diagrams for a configuration of a wirelesscommunication system having multiple antennas;

FIG. 6 illustrates a subframe in which a D2D synchronization signal istransmitted;

FIG. 7 is a diagram for explaining relay of a D2D signal;

FIGS. 8A and 8B are diagrams for an example of a D2D resource pool forD2D communication;

FIG. 9 is a diagram for explaining an SA period;

FIGS. 10 to 15B are diagrams illustrating transmission timing ofACK/NACK according to each embodiment of the present invention;

FIGS. 16A to 17B are diagrams illustrating an SCI transmission resourceaccording to an embodiment of the present invention;

FIG. 18 is a diagram for configurations of a transmitter and a receiver.

DETAILED DESCRIPTION

The embodiments of the present invention described hereinbelow arecombinations of elements and features of the present invention. Theelements or features may be considered selective unless otherwisementioned. Each element or feature may be practiced without beingcombined with other elements or features. Further, an embodiment of thepresent invention may be constructed by combining parts of the elementsand/or features. Operation orders described in embodiments of thepresent invention may be rearranged. Some constructions or features ofany one embodiment may be included in another embodiment and may bereplaced with corresponding constructions or features of anotherembodiment.

In the embodiments of the present invention, a description is made,centering on a data transmission and reception relationship between aBase Station (BS) and a User Equipment (UE). The BS is a terminal nodeof a network, which communicates directly with a UE. In some cases, aspecific operation described as performed by the BS may be performed byan upper node of the BS.

Namely, it is apparent that, in a network comprised of a plurality ofnetwork nodes including a BS, various operations performed forcommunication with a UE may be performed by the BS or network nodesother than the BS. The term ‘BS’ may be replaced with the term ‘fixedstation’, ‘Node B’, ‘evolved Node B (eNode B or eNB)’, ‘Access Point(AP)’, etc. The term ‘relay’ may be replaced with the term ‘Relay Node(RN)’ or ‘Relay Station (RS)’. The term ‘terminal’ may be replaced withthe term ‘UE’, ‘Mobile Station (MS)’, ‘Mobile Subscriber Station (MSS)’,‘Subscriber Station (SS)’, etc.

The term “cell”, as used herein, may be applied to transmission andreception points such as a base station (eNB), sector, remote radio head(RRH) and relay, and may also be extensively used by a specifictransmission/reception point to distinguish between component carriers.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention can be supported by standarddocuments disclosed for at least one of wireless access systems,Institute of Electrical and Electronics Engineers (IEEE) 802, 3rdGeneration Partnership Project (3GPP), 3GPP Long Term Evolution (3GPPLTE), LTE-Advanced (LTE-A), and 3GPP2. Steps or parts that are notdescribed to clarify the technical features of the present invention canbe supported by those documents. Further, all terms as set forth hereincan be explained by the standard documents.

Techniques described herein can be used in various wireless accesssystems such as Code Division Multiple Access (CDMA), Frequency DivisionMultiple Access (FDMA), Time Division Multiple Access (TDMA), OrthogonalFrequency Division Multiple Access (OFDMA), Single Carrier-FrequencyDivision Multiple Access (SC-FDMA), etc. CDMA may be implemented as aradio technology such as Universal Terrestrial Radio Access (UTRA) orCDMA2000. TDMA may be implemented as a radio technology such as GlobalSystem for Mobile communications (GSM)/General Packet Radio Service(GPRS)/Enhanced Data Rates for GSM Evolution (EDGE). OFDMA may beimplemented as a radio technology such as IEEE 802.11 (Wi-Fi), IEEE802.16 (WiMAX), IEEE 802.20, Evolved-UTRA (E-UTRA) etc. UTRA is a partof Universal Mobile Telecommunications System (UMTS). 3GPP LTE is a partof Evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE employs OFDMA fordownlink and SC-FDMA for uplink. LTE-A is an evolution of 3GPP LTE.WiMAX can be described by the IEEE 802.16e standard (WirelessMetropolitan Area Network (WirelessMAN)-OFDMA Reference System) and theIEEE 802.16m standard (WirelessMAN-OFDMA Advanced System). For clarity,this application focuses on the 3GPP LTE and LTE-A systems. However, thetechnical features of the present invention are not limited thereto.

LTE/LTE-A Resource Structure/Channel

With reference to FIGS. 1A and 1B, the structure of a radio frame willbe described below.

In a cellular Orthogonal Frequency Division Multiplexing (OFDM) wirelessPacket communication system, uplink and/or downlink data Packets aretransmitted in subframes. One subframe is defined as a predeterminedtime period including a plurality of OFDM symbols. The 3GPP LTE standardsupports a type-1 radio frame structure applicable to Frequency DivisionDuplex (FDD) and a type-2 radio frame structure applicable to TimeDivision Duplex (TDD).

FIG. 1A illustrates the type-1 radio frame structure. A downlink radioframe is divided into 10 subframes. Each subframe is further dividedinto two slots in the time domain. A unit time during which one subframeis transmitted is defined as a Transmission Time Interval (TTI). Forexample, one subframe may be 1 ms in duration and one slot may be 0.5 msin duration. A slot includes a plurality of OFDM symbols in the timedomain and a plurality of Resource Blocks (RBs) in the frequency domain.Because the 3GPP LTE system adopts OFDMA for downlink, an OFDM symbolrepresents one symbol period. An OFDM symbol may be referred to as anSC-FDMA symbol or symbol period. An RB is a resource allocation unitincluding a plurality of contiguous subcarriers in a slot.

The number of OFDM symbols in one slot may vary depending on a CyclicPrefix (CP) configuration. There are two types of CPs: extended CP andnormal CP. In the case of the normal CP, one slot includes 7 OFDMsymbols. In the case of the extended CP, the length of one OFDM symbolis increased and thus the number of OFDM symbols in a slot is smallerthan in the case of the normal CP. Thus when the extended CP is used,for example, 6 OFDM symbols may be included in one slot. If channelstate gets poor, for example, during fast movement of a UE, the extendedCP may be used to further decrease Inter-Symbol Interference (ISI).

In the case of the normal CP, one subframe includes 14 OFDM symbolsbecause one slot includes 7 OFDM symbols. The first two or three OFDMsymbols of each subframe may be allocated to a Physical Downlink ControlCHannel (PDCCH) and the other OFDM symbols may be allocated to aPhysical Downlink Shared Channel (PDSCH).

FIG. 1B illustrates the type-2 radio frame structure. A type-2 radioframe includes two half frames, each having 5 subframes, a DownlinkPilot Time Slot (DwPTS), a Guard Period (GP), and an Uplink Pilot TimeSlot (UpPTS). Each subframe is divided into two slots. The DwPTS is usedfor initial cell search, synchronization, or channel estimation at a UE.The UpPTS is used for channel estimation and acquisition of uplinktransmission synchronization to a UE at an eNB. The GP is a periodbetween an uplink and a downlink, which eliminates uplink interferencecaused by multipath delay of a downlink signal. One subframe includestwo slots irrespective of the type of a radio frame.

The above-described radio frame structures are purely exemplary and thusit is to be noted that the number of subframes in a radio frame, thenumber of slots in a subframe, or the number of symbols in a slot mayvary.

FIG. 2 illustrates the structure of a downlink resource grid for theduration of one downlink slot. A downlink slot includes 7 OFDM symbolsin the time domain and an RB includes 12 subcarriers in the frequencydomain, which does not limit the scope and spirit of the presentinvention. For example, a downlink slot may include 7 OFDM symbols inthe case of the normal CP, whereas a downlink slot may include 6 OFDMsymbols in the case of the extended CP. Each element of the resourcegrid is referred to as a Resource Element (RE). An RB includes 12×7 REs.The number of RBs in a downlink slot, NDL depends on a downlinktransmission bandwidth. An uplink slot may have the same structure as adownlink slot.

FIG. 3 illustrates the structure of a downlink subframe. Up to threeOFDM symbols at the start of the first slot in a downlink subframe areused for a control region to which control channels are allocated andthe other OFDM symbols of the downlink subframe are used for a dataregion to which a PDSCH is allocated. Downlink control channels used inthe 3GPP LTE system include a Physical Control Format Indicator CHannel(PCFICH), a Physical Downlink Control CHannel (PDCCH), and a PhysicalHybrid automatic repeat request (HARQ) Indicator CHannel (PHICH). ThePCFICH is located in the first OFDM symbol of a subframe, carryinginformation about the number of OFDM symbols used for transmission ofcontrol channels in the subframe. The PHICH delivers an HARQACKnowledgment/Negative ACKnowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled Downlink Control Information (DCI). The DCI transports uplink ordownlink scheduling information, or uplink transmission power controlcommands for UE groups. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared CHannel(DL-SCH), resource allocation information about an Uplink Shared CHannel(UL-SCH), paging information of a Paging CHannel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregatingone or more consecutive Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE includes a plurality of REgroups. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH is for a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 4 illustrates the structure of an uplink subframe. An uplinksubframe may be divided into a control region and a data region in thefrequency domain. A Physical Uplink Control CHannel (PUCCH) carryinguplink control information is allocated to the control region and aPhysical Uplink Shared Channel (PUSCH) carrying user data is allocatedto the data region. To maintain the property of a single carrier, a UEdoes not transmit a PUSCH and a PUCCH simultaneously. A PUCCH for a UEis allocated to an RB pair in a subframe. The RBs of the RB pair occupydifferent subcarriers in two slots. Thus it is said that the RB pairallocated to the PUCCH is frequency-hopped over a slot boundary.

Reference Signals (RSs)

In a wireless communication system, a Packet is transmitted on a radiochannel. In view of the nature of the radio channel, the Packet may bedistorted during the transmission. To receive the signal successfully, areceiver should compensate for the distortion of the received signalusing channel information. Generally, to enable the receiver to acquirethe channel information, a transmitter transmits a signal known to boththe transmitter and the receiver and the receiver acquires knowledge ofchannel information based on the distortion of the signal received onthe radio channel. This signal is called a pilot signal or an RS.

In the case of data transmission and reception through multipleantennas, knowledge of channel states between Transmission (Tx) antennasand Reception (Rx) antennas is required for successful signal reception.Accordingly, an RS should be transmitted through each Tx antenna.

RSs may be divided into downlink RSs and uplink RSs. In the current LTEsystem, the uplink RSs include:

i) DeModulation-Reference Signal (DM-RS) used for channel estimation forcoherent demodulation of information delivered on a PUSCH and a PUCCH;and

ii) Sounding Reference Signal (SRS) used for an eNB or a network tomeasure the quality of an uplink channel in a different frequency.

The downlink RSs are categorized into:

i) Cell-specific Reference Signal (CRS) shared among all UEs of a cell;

ii) UE-specific RS dedicated to a specific UE;

iii) DM-RS used for coherent demodulation of a PDSCH, when the PDSCH istransmitted;

iv) Channel State Information-Reference Signal (CSI-RS) carrying CSI,when downlink DM-RSs are transmitted;

v) Multimedia Broadcast Single Frequency Network (MB SFN) RS used forcoherent demodulation of a signal transmitted in MB SFN mode; and

vi) positioning RS used to estimate geographical position informationabout a UE.

RSs may also be divided into two types according to their purposes: RSfor channel information acquisition and RS for data demodulation. Sinceits purpose lies in that a UE acquires downlink channel information, theformer should be transmitted in a broad band and received even by a UEthat does not receive downlink data in a specific subframe. This RS isalso used in a situation like handover. The latter is an RS that an eNBtransmits along with downlink data in specific resources. A UE candemodulate the data by measuring a channel using the RS. This RS shouldbe transmitted in a data transmission area.

Modeling of MIMO System

FIGS. 5A and 5B are diagrams illustrating a configuration of a wirelesscommunication system having multiple antennas.

As shown in FIG. 5A, if the number of transmit antennas is increased toNT and the number of receive antennas is increased to NR, a theoreticalchannel transmission capacity is increased in proportion to the numberof antennas, unlike the case where a plurality of antennas is used inonly a transmitter or a receiver. Accordingly, it is possible to improvea transfer rate and to remarkably improve frequency efficiency. As thechannel transmission capacity is increased, the transfer rate may betheoretically increased by a product of a maximum transfer rate Ro uponutilization of a single antenna and a rate increase ratio Ri.

R _(i)=min(N _(T) ,N _(R))  Equation 1

For instance, in an MIMO communication system, which uses 4 transmitantennas and 4 receive antennas, a transmission rate 4 times higher thanthat of a single antenna system can be obtained. Since this theoreticalcapacity increase of the MIMO system has been proved in the middle of90's, many ongoing efforts are made to various techniques tosubstantially improve a data transmission rate. In addition, thesetechniques are already adopted in part as standards for various wirelesscommunications such as 3G mobile communication, next generation wirelessLAN and the like.

The trends for the MIMO relevant studies are explained as follows. Firstof all, many ongoing efforts are made in various aspects to develop andresearch information theory study relevant to MIMO communicationcapacity calculations and the like in various channel configurations andmultiple access environments, radio channel measurement and modelderivation study for MIMO systems, spatiotemporal signal processingtechnique study for transmission reliability enhancement andtransmission rate improvement and the like.

In order to explain a communicating method in an MIMO system in detail,mathematical modeling can be represented as follows. It is assumed thatthere are NT transmit antennas and NR receive antennas.

Regarding a transmitted signal, if there are NT transmit antennas, themaximum number of pieces of information that can be transmitted is NT.Hence, the transmission information can be represented as shown inEquation 2.

s=└s ₁ ,s ₂ , . . . ,s _(N) _(T) ┘^(T)  Equation 2

Meanwhile, transmit powers can be set different from each other forindividual pieces of transmission information s₁, s₂, . . . , s_(N) _(T), respectively. If the transmit powers are set to P₁, P₂, . . . P_(N)_(T) , respectively, the transmission information with adjusted transmitpowers can be represented as Equation 3.

ŝ=[ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ]^(T)=[P ₁ s ₁ ,P ₂ s ₂ , . . . ,P _(N)_(T) s _(N) _(T) ]^(T)  Equation 3

In addition, Ŝ can be represented as Equation 4 using diagonal matrix Pof the transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}s_{1} \\s_{2} \\\vdots \\s_{N_{T}}\end{bmatrix}} = {Ps}}} & {{Equation}\mspace{14mu} 4}\end{matrix}$

Assuming a case of configuring NT transmitted signals x₁, x₂, . . . ,x_(N) _(T) , which are actually transmitted, by applying weight matrix Wto the information vector Ŝ having the adjusted transmit powers, theweight matrix W serves to appropriately distribute the transmissioninformation to each antenna according to a transport channel state. x₁,x₂, . . . , x_(N) _(T) can be expressed by using the vector X asfollows.

                                      Equation  5$x = {\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix} = {{\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{21} & w_{22} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i1} & w_{i2} & \ldots & w_{iN_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\mspace{11mu}\begin{bmatrix}{\overset{\hat{}}{s}}_{1} \\{\overset{\hat{}}{s}}_{2} \\\vdots \\{\overset{\hat{}}{s}}_{j} \\\vdots \\{\overset{\hat{}}{s}}_{N_{T}}\end{bmatrix}} = {{W\overset{\hat{}}{s}} = {WPs}}}}$

In Equation 5, w_(ij) denotes a weight between an i^(th) transmitantenna and j^(th) information. W is also called a precoding matrix.

If the NR receive antennas are present, respective received signals y₁,y₂, . . . , y_(N) _(R) of the antennas can be expressed as follows.

y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  Equation 6

If channels are modeled in the MIMO wireless communication system, thechannels may be distinguished according to transmit/receive antennaindexes. A channel from the transmit antenna j to the receive antenna iis denoted by h_(ij). In h_(ij), it is noted that the indexes of thereceive antennas precede the indexes of the transmit antennas in view ofthe order of indexes.

FIG. 5B is a diagram illustrating channels from the NT transmit antennasto the receive antenna i. The channels may be combined and expressed inthe form of a vector and a matrix. In FIG. 5B, the channels from the NTtransmit antennas to the receive antenna i can be expressed as follows.

h _(i) ^(T)=[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  Equation 7

Accordingly, all channels from the NT transmit antennas to the NRreceive antennas can be expressed as follows.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{2N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \ddots & \ddots & \; \\h_{i\; 1} & h_{i2} & \ldots & h_{iN_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & {{Equation}\mspace{14mu} 8}\end{matrix}$

An AWGN (Additive White Gaussian Noise) is added to the actual channelsafter a channel matrix H. The AWGN n₁, n₂, . . . , n_(N) _(R)respectively added to the NR receive antennas can be expressed asfollows.

n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  Equation 9

Through the above-described mathematical modeling, the received signalscan be expressed as follows.

                                      Equation  10$y = {\begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix} = {{{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{21} & h_{22} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 1} & h_{i2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\mspace{11mu}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}} = {{Hx} + n}}}$

Meanwhile, the number of rows and columns of the channel matrix Hindicating the channel state is determined by the number of transmit andreceive antennas. The number of rows of the channel matrix H is equal tothe number NR of receive antennas and the number of columns thereof isequal to the number NR of transmit antennas. That is, the channel matrixH is an NR×NT matrix.

The rank of the matrix is defined by the smaller of the number of rowsand the number of columns, which are independent from each other.Accordingly, the rank of the matrix is not greater than the number ofrows or columns. The rank rank(H) of the channel matrix H is restrictedas follows.

rank(H)≤min(N _(T) ,N _(R))  Equation 11

Additionally, the rank of a matrix can also be defined as the number ofnon-zero Eigen values when the matrix is Eigen-value-decomposed.Similarly, the rank of a matrix can be defined as the number of non-zerosingular values when the matrix is singular-value-decomposed.Accordingly, the physical meaning of the rank of a channel matrix can bethe maximum number of channels through which different pieces ofinformation can be transmitted.

In the description of the present document, ‘rank’ for MIMO transmissionindicates the number of paths capable of sending signals independentlyon specific time and frequency resources and ‘number of layers’indicates the number of signal streams transmitted through therespective paths. Generally, since a transmitting end transmits thenumber of layers corresponding to the rank number, one rank has the samemeaning of the layer number unless mentioned specially.

Synchronization Acquisition of D2D UE

Now, a description will be given of synchronization acquisition betweenUEs in D2D communication based on the foregoing description in thecontext of the legacy LTE/LTE-A system. In an OFDM system, iftime/frequency synchronization is not acquired, the resulting Inter-CellInterference (ICI) may make it impossible to multiplex different UEs inan OFDM signal. If each individual D2D UE acquires synchronization bytransmitting and receiving a synchronization signal directly, this isinefficient. In a distributed node system such as a D2D communicationsystem, therefore, a specific node may transmit a representativesynchronization signal and the other UEs may acquire synchronizationusing the representative synchronization signal. In other words, somenodes (which may be an eNB, a UE, and a Synchronization Reference Node(SRN, also referred to as a synchronization source)) may transmit a D2DSynchronization Signal (D2DSS) and the remaining UEs may transmit andreceive signals in synchronization with the D2DSS.

D2DSSs may include a Primary D2DSS (PD2DSS) or a Primary SidelinkSynchronization Signal (PSSS) and a Secondary D2DSS (SD2DSS) or aSecondary Sidelink Synchronization Signal (SSSS). The PD2DSS may beconfigured to have a similar/modified/repeated structure of a Zadoff-chusequence of a predetermined length or a Primary Synchronization Signal(PSS). Unlike a DL PSS, the PD2DSS may use a different Zadoff-chu rootindex (e.g., 26, 37). And, the SD2DSS may be configured to have asimilar/modified/repeated structure of an M-sequence or a SecondarySynchronization Signal (SSS). If UEs synchronize their timing with aneNB, the eNB serves as an SRN and the D2DSS is a PSS/SSS. Unlike PSS/SSSof DL, the PD2DSS/SD2DSS follows UL subcarrier mapping scheme. FIG. 6shows a subframe in which a D2D synchronization signal is transmitted. APhysical D2D Synchronization Channel (PD2DSCH) may be a (broadcast)channel carrying basic (system) information that a UE should firstobtain before D2D signal transmission and reception (e.g., D2DSS-relatedinformation, a Duplex Mode (DM), a TDD UL/DL configuration, a resourcepool-related information, the type of an application related to theD2DSS, etc.). The PD2DSCH may be transmitted in the same subframe as theD2DSS or in a subframe subsequent to the frame carrying the D2DSS. ADMRS can be used to demodulate the PD2DSCH.

The SRN may be a node that transmits a D2DSS and a PD2DSCH. The D2DSSmay be a specific sequence and the PD2DSCH may be a sequencerepresenting specific information or a codeword produced bypredetermined channel coding. The SRN may be an eNB or a specific D2DUE. In the case of partial network coverage or out of network coverage,the SRN may be a UE.

In a situation illustrated in FIG. 7, a D2DSS may be relayed for D2Dcommunication with an out-of-coverage UE. The D2DSS may be relayed overmultiple hops. The following description is given with the appreciationthat relay of an SS covers transmission of a D2DSS in a separate formataccording to a SS reception time as well as direct Amplify-and-Forward(AF)-relay of an SS transmitted by an eNB. As the D2DSS is relayed, anin-coverage UE may communicate directly with an out-of-coverage UE.

D2D Resource Pool

FIGS. 8A and 8B show an example of a UE1, a UE2 and a resource pool usedby the UE1 and the UE2 performing D2D communication. In FIG. 8A, a UEcorresponds to a terminal or such a network device as an eNBtransmitting and receiving a signal according to a D2D communicationscheme. A UE selects a resource unit corresponding to a specificresource from a resource pool corresponding to a set of resources andthe UE transmits a D2D signal using the selected resource unit. A UE2corresponding to a reception UE receives a configuration of a resourcepool in which the UE1 is able to transmit a signal and detects a signalof the UE1 in the resource pool. In this case, if the UE1 is located atthe inside of coverage of an eNB, the eNB can inform the UE1 of theresource pool. If the UE1 is located at the outside of coverage of theeNB, the resource pool can be informed by a different UE or can bedetermined by a predetermined resource. In general, a resource poolincludes a plurality of resource units. A UE selects one or moreresource units from among a plurality of the resource units and may beable to use the selected resource unit(s) for D2D signal transmission.FIG. 8B shows an example of configuring a resource unit. Referring toFIG. 8B, the entire frequency resources are divided into the NF numberof resource units and the entire time resources are divided into the NTnumber of resource units. In particular, it is able to define NF*NTnumber of resource units in total. In particular, a resource pool can berepeated with a period of NT subframes. Specifically, as shown in FIGS.8A and 8B, one resource unit may periodically and repeatedly appear. Or,an index of a physical resource unit to which a logical resource unit ismapped may change with a predetermined pattern according to time toobtain a diversity gain in time domain and/or frequency domain. In thisresource unit structure, a resource pool may correspond to a set ofresource units capable of being used by a UE intending to transmit a D2Dsignal.

A resource pool can be classified into various types. First of all, theresource pool can be classified according to contents of a D2D signaltransmitted via each resource pool. For example, the contents of the D2Dsignal can be classified into various signals and a separate resourcepool can be configured according to each of the contents. The contentsof the D2D signal may include SA (scheduling assignment), a D2D datachannel, and a discovery channel. The SA may correspond to a signalincluding information on a resource position of a D2D data channel,information on MCS (modulation and coding scheme) necessary formodulating and demodulating a data channel, information on a MIMOtransmission scheme, information on TA (timing advance), and the like.The SA signal can be transmitted on an identical resource unit in amanner of being multiplexed with D2D data. In this case, an SA resourcepool may correspond to a pool of resources that an SA and D2D data aretransmitted in a manner of being multiplexed. The SA signal can also bereferred to as a D2D control channel or a PSCCH (physical sidelinkcontrol channel). The D2D data channel (or, PSSCH (physical sidelinkshared channel)) corresponds to a resource pool used by a transmissionUE to transmit user data. If an SA and a D2D data are transmitted in amanner of being multiplexed in an identical resource unit, D2D datachannel except SA information can be transmitted only in a resource poolfor the D2D data channel. In other word, resource elements (REs), whichare used to transmit SA information in a specific resource unit of an SAresource pool, can also be used for transmitting D2D data in a D2D datachannel resource pool. The discovery channel may correspond to aresource pool for a message that enables a neighboring UE to discovertransmission UE transmitting information such as ID of the UE, and thelike.

Although contents of D2D signal are identical to each other, it may usea different resource pool according to a transmission/receptionattribute of the D2D signal. For example, in case of the same D2D datachannel or the same discovery message, the D2D data channel or thediscovery signal can be classified into a different resource poolaccording to a transmission timing determination scheme (e.g., whether aD2D signal is transmitted at the time of receiving a synchronizationreference signal or the timing to which a prescribed timing advance isadded) of a D2D signal, a resource allocation scheme (e.g., whether atransmission resource of an individual signal is designated by an eNB oran individual transmission UE selects an individual signal transmissionresource from a pool), a signal format (e.g., number of symbols occupiedby a D2D signal in a subframe, number of subframes used for transmittinga D2D signal), signal strength from an eNB, strength of transmit powerof a D2D UE, and the like. For clarity, a method for an eNB to directlydesignate a transmission resource of a D2D transmission UE is referredto as a mode 1. If a transmission resource region is configured inadvance or an eNB designates the transmission resource region and a UEdirectly selects a transmission resource from the transmission resourceregion, it is referred to as a mode 2. In case of performing D2Ddiscovery, if an eNB directly indicates a resource, it is referred to asa type 2. If a UE directly selects a transmission resource from apredetermined resource region or a resource region indicated by the eNB,it is referred to as a type 1.

Transmission and Reception of SA

A mode 1 UE can transmit an SA signal (or, a D2D control signal, SCI(sidelink control information)) via a resource configured by an eNB. Amode 2 UE receives a configured resource to be used for D2Dtransmission. The mode 2 UE can transmit SA by selecting a timefrequency resource from the configured resource.

The SA period can be defined as FIG. 9. Referring to FIG. 9, a first SAperiod can start at a subframe apart from a specific system frame asmuch as a prescribed offset (SAOffsetIndicator) indicated by higherlayer signaling. Each SA period can include an SA resource pool and asubframe pool for transmitting D2D data. The SA resource pool caninclude subframes ranging from a first subframe of an SA period to thelast subframe among subframes indicated by a subframe bitmap(saSubframeBitmap) to transmit SA. In case of mode 1, T-RPT(time-resource pattern for transmission) is applied to the resource poolfor transmitting D2D data to determine a subframe in which an actualdata is transmitted. As shown in the drawing, if the number of subframesincluded in an SA period except the SA resource pool is greater than thenumber of T-RPT bits, the T-RPT can be repeatedly applied and the lastlyapplied T-RPT can be applied in a manner of being truncated as many asthe number of remaining subframes. A transmission UE performstransmission at a position where a T-RPT bitmap corresponds to 1 in anindicated T-RPT and 4 transmissions are performed in a MAC PDU.

Meanwhile, in V2V (vehicle-to-vehicle) communication, a CAM (CooperativeAwareness Message) of a periodic message type, a DENM (DecentralizedEnvironmental Notification Message) of an event triggered message typeand the like can be transmitted. The CAM contains the basic vehicleinformation, including vehicle dynamic status information like directionand speed, vehicle static data like dimension, status of exteriorlights, path history. The size of CAM message is between 50-300 Bytes.The DENM may correspond to a message which is generated when such anunexpected situation as a malfunction of a car, an accident, and thelike occurs. The size of DENM is smaller than 3000 Bytes. All carswithin the transmission range can receive the message. In this case, theDENM may have a priority higher than a priority of the CAM. In thiscase, when a message has a higher priority, it means that the message ofthe higher priority is preferentially transmitted in the aspect of a UEwhen messages are transmitted at the same time. Or, it means that themessage of the higher priority is preferentially transmitted in timeamong a plurality of messages. In the aspect of a plurality of UEs, itmay be able to make the message of the higher priority receive lessinterference compared to a message of a lower priority to reduce areception error probability. If security overhead is included in theCAM, the CAM may have a bigger message size.

In the following, a method of transmitting HARQ (Hybrid automatic repeatrequest) ACK (acknowledgement)/NACK (Negative acknowledgement) (orACK/NACK), a method of configuring transmit power between UEs and thelike capable of being applied to D2D communication, V2X communication,and communication between MTC UEs or between an MTC UE and a relay UEare explained.

Method of Transmitting ACK/NACK

First Method of Determining Timing at which ACK/NACK is Transmitted

According to one embodiment of the present invention, a second UE candetermine a subframe in which ACK/NACK is to be transmitted by receivingdata from a first UE and comparing a T-RPT of the first UE with a T-RPTof the second UE. When the second UE compares the T-RPT of the first UEwith the T-RPT of the second UE, the second UE can perform thecomparison on subframes appearing after a k^(th) subframe from asubframe in which data is received. The second UE can determine a firstsubframe of which the T-RPT of the first UE corresponds to 0 and theT-PRT of the second UE corresponds to 1 as a subframe in which ACK/NACKis to be transmitted among the subframes appearing after the k^(th)subframe. The k can be configured by a number such as 4 in advance orcan be forwarded to a UE via higher layer/physical layer signaling (thiscan be identically applied to the following description). The second UEcan transmit ACK/NACK to the first UE in the determined subframe inresponse to the received data.

In particular, as shown in FIG. 10, when a data is received in asubframe # n, ACK/NACK transmission can be performed in a first Txsubframe appearing after a subframe #(n+4) and the Tx subframe notoverlapped with Tx of a UE1 (transmission UE).

When a subframe in which ACK/NACK is to be transmitted is not determinedby comparing T-RPT of a transmission UE with T-RPT of a reception UE,ACK/NACK can be transmitted in a subframe #(n+4) appearing after asubframe in which data is received similar to communication with an eNB.In this case, if a T-RPT value of a data transmission UE corresponds to1 (i.e., if the data transmission UE performs transmission), the datatransmission UE is unable to receive ACK/NACK. In particular, it is ableto solve half-duplex constraint related to ACK/NACK transmission withthe help of the configuration above.

In the foregoing description, although it is assumed that ACK/NACK istransmitted one time, ACK/NACK can be repeatedly transmitted a times. Inparticular, the second UE can repeatedly transmit ACK/NACK in the anumber of subframes where a T-RPT value of the second UE corresponds to1 after the first subframe. This method does not consider a T-RPT of thefirst UE in retransmission. Since ACK/NACK has already been transmittedin consideration of a transmission of the first UE, retransmission putsemphasis on fast transmission. Or, the second UE can repeatedly transmitACK/NACK in the a number of subframes where a T-RPT value of the firstUE corresponds to 0 and a T-RPT value of the second UE corresponds to 1appearing after the first subframe. In particular, ACK/NACK istransmitted in consideration of the T-RPT of the first UE inretransmission. In particular, reception success of ACK/NACK isimportant in the present method. The retransmission/repetitivetransmission of ACK/NACK can also be used for other embodimentsdescribed in the following. (For example, as shown in FIG. 11, whenACK/NACK is transmitted in a first Tx subframe appearing after asubframe #(n+4), repetitive transmission can be repeated 3 times in asubframe where a T-RPT value corresponds to 1.) A method to be usedamong the abovementioned two retransmission methods can be configured inadvance or can be forwarded via higher layer/physical layer signaling.

Meanwhile, T-RPT of the first UE and T-RPT of the second UE can bedetermined by the first UE and the second UE, respectively. In thiscase, if the first UE and the second UE randomly select a T-RPT, hugenumbers of cases may occur. In this case, since it is difficult for a UEto anticipate the maximum number of ACK/NACK to be transmitted in aspecific subframe, it is difficult for the UE to determine the number ofREs to be reserved when piggyback is performed on ACK/NACK. In order toprevent this, the second UE may use a T-RPT selected by the first UE andthe T-RPT on which (circular) time shift is performed only. Inparticular, a T-RPT of the second UE may correspond to a T-RPT thatcircular shift as much as a predetermined value is performed on theT-RPT of the first UE. Or, it may be able to define a rule that thesecond UE uses a TRP of a specific pattern (e.g., a space of is isconstant, the number of is is equal to or greater (less) than aprescribed number) only. For example, the number of is included in theT-RPT of the second UE can be included in a predetermined range. Theabovementioned T-RPT selection can also be applied to other embodimentsdescribed in the following.

Second Method of Determining Timing at which ACK/NACK is Transmitted

The second UE can transmit ACK/NACK in a first subframe where a T-RPTvalue corresponds to 1 appearing after n+k from a subframe in which datais received. In particular, as shown in FIG. 12, when a data is receivedin a subframe # n, ACK/NACK can be transmitted in a first Tx subframe(subframe #(n+6)) appearing after n+4 from the subframe # n.

Third Method of Determining Timing at which ACK/NACK is Transmitted

The second UE can perform ACK/NACK transmission in a unit of MAC PDU.Specifically, as shown in FIG. 13, if the last Tx subframe of MAC PDUcorresponds to a subframe # n, ACK/NACK can be transmitted in a first Txsubframe appearing after a subframe #(n+4). Moreover, as mentionedearlier in the first method of determining ACK/NACK transmission timing,when a subframe in which transmission is performed by the first UE isdetermined by comparing T-RPT of the first UE with T-RPT of the secondUE, ACK/NACK can be transmitted in a subframe not overlapped with thesubframe.

Fourth Method of Determining Timing at which ACK/NACK is Transmitted

ACK/NACK can be transmitted at a time in response to all data receivedwithin a corresponding SC (sidelink control)/SA period in the last Txsubframe of the second UE. In particular, as shown in FIG. 14, thesecond UE can transmit ACK/NACK at a time in response to all datareceived within SC period/SA period in the last Tx subframe within theSC period/SA period. In this case, Tx overlap with the first UE mayoccur. Hence, ACK/NACK can be transmitted in the last Tx subframe notoverlapped with the first UE. In this case, all ACK/NACK can betransmitted in a manner of being bundled, the ACK/NACK are transmittedin a manner of being bundled in a MAC PDU unit, or the ACK/NACK can beseparately transmitted in response to packets of all receptionsubframes.

Fifth Method of Determining Timing at which ACK/NACK is Transmitted

Meanwhile, ACK/NACK can be transmitted in every data Tx subframe (SCIpiggyback). In this case, it may be able to configure a timingrelationship by designating a data subframe related to the ACK/NACK. Forexample, as shown in FIG. 15A, when ACK/NACK is transmitted in a Txsubframe # n, the ACK/NACK is related to a subframe received in asubframe closest to a subframe #(n−4) (in particular, Tx subframe isnaturally excluded). As mentioned earlier in the first method ofdetermining ACK/NACK transmission timing in FIG. 15A, when a subframe inwhich transmission is performed by the first UE is determined bycomparing T-RPT of the first UE with T-RPT of the second UE, FIG. 15Billustrates a case of applying ACK/NACK transmission in a subframe notoverlapped with the subframe.

Meanwhile, a CSI measurement value can be transmitted together at theproposed ACK/NACK transmission timing. In particular, a subframe inwhich ACK/NACK is transmitted can include most recently received controlinformation prior to the subframe or channel state information on data.For example, in FIGS. 15A and 15B, when ACK/NACK is transmitted in asubframe # n, if the ACK/NACK is transmitted in a subframe receivedprior to a subframe #(n−4) (including the subframe #(n−4)), it may beable to feedback CSI which is obtained by measuring a DMRS of a mostrecently received PSSCH/PSDCH in the subframe #(n−4).

Meanwhile, when a plurality of subframes are received, ACK/NACK can beindividually transmitted in response to each of a plurality of thesubframes. Or, ACK/NACK can be transmitted by applying A/N bundling(logical AND operation). Or, ACK/NACK can be transmitted in a manner ofbeing bundled according to MAC PDU. When ACK/NACK are piggybacked, inorder to indicate the number of ACK/NACK to be transmitted, informationon the total number of ACK/NACK can be transmitted together.

Each of the embodiments can be applied to a case that SCI is transmittedin a data region in a manner of being piggybacked.

SCI (Sidelink Control Information) Contents and Transmission Resource

In the following, a method of transmitting SCI is proposed. According tothe method, it is able to solve a problem of failing to receive feedbackfor data transmission, i.e., ACK/NACK, due to half-duplex constraint.

It may be able to transmit SCI (ACK/NACK, CSI, power control, RI, MIMOprecoding information, and the like) via a separately allocated resourceregion. Specifically, a region identical to a PSCCH region or anadditional PSCCH region (additional SCI resource pool or subframe ofFIGS. 16A and 16B) is configured and SCI such as ACK/NACK, CSI, powercontrol, and the like can be transmitted in the resource region.According to the method above, it may be able to have a merit in that itis able to reuse a resource region similar to a legacy SA resource pool.Since information such as ACK/NACK, CSI, and power control is notrelevant to resource allocation of data, the information can be arrangedafter a data resource pool. If information such as ACK/NACK and CSI istransmitted together in a legacy SA resource, SCI information can betransmitted in a manner of being piggybacked by performing puncturing orrate matching on a partial RE in a PSCCH region.

Or, ACK/NACK or CSI information can be transmitted in a manner of beingincluded in a new field by defining an additional PSCCH format. Or, asshown in FIGS. 16A and 16B, it may be able to configure an additionalresource pool for transmitting SCI after a legacy SA pool. Theadditional pool can be used for receiving ACK/NACK in response to dataof a previous SC period. The additional SCI resource region can beconfigured for ACK/NACK, CSI, power control, and the like allocated in aprevious data pool. In the resource region, it may be able to define anew format. In particular, although a length of a PSCCH format isidentical to a length of a legacy PSCCH format, a contents field can bedifferently configured. Or, it may be able to define an additionalphysical layer format. For example, unlike the legacy PSCCH format, theadditional physical layer format can be configured in a unit of 2 RBs oran RB size can be configured by a network. When SCI is transmitted inthe additional SA resource region, ACK/NACK can be transmitted inresponse to received packets in a data region interlocked with theadditional SA resource region. In this case, the ACK/NACK can betransmitted by bundling all of ACK/NACK for each received packet, theACK/NACK can be transmitted by bundling the ACK/NACK in a MAC PDU unit,or the ACK/NACK can be transmitted in response to an individuallyreceived packet.

As a different method, it may be able to transmit SCI by piggybackingthe SCI in data transmission within the same SA period. To this end, atransmission UE (first UE) can separately transmit SA for a datareception UE (second UE=ACK/NACK transmission UE, or data reception UE).Specifically, there are a method for the first UE to transmit SA of thesecond UE as well and a method for the first UE and the second UE totransmit SA, respectively.

FIG. 17A illustrates a case that the first UE transmits both SA fortransmitting data of the first UE and SA (indicating a resource fortransmitting ACK/NACK of the second UE) for receiving ACK/NACK. Thesecond UE can transmit ACK/NACK to the first UE using a resourceindicated by the SA for receiving ACK/NACK. In this case, since thefirst UE transmits both of the SAs, the method has a merit in that it isnot necessary to worry about a half-duplex constraint with the SA of thesecond UE. It is O.K. to transmit the SAs of the two UEs in the samesubframe.

FIG. 17B illustrates a case that the second UE autonomously transmitsSA. In this case, when the second UE receives SA transmitted by thefirst UE, in order for the second UE to determine a TRP based on thereceived SA, a plurality of SA pools can be configured. For example, anSA pool (SA resource pool #1) for transmitting data and an SA pool (SAresource pool #2) for transmitting SCI can be separately configured.According to the method, since the second UE monitors the SA of thefirst UE and is able to modify SA contents, degree of freedom of thesecond UE is increased compared to the method that the first UEtransmits SA of the second UE. A network can indicate a UE and an SApool to be used by the UE. Or, a UE can autonomously determine an SApool to be used by the UE. A UE can inform a neighboring UE of an SApool to be used in a next SC period via physical layer signaling orhigher layer signaling.

In the foregoing description, the first UE may correspond to an R-UE(Relay UE) and the second UE may correspond to an M-UE (MTC (MachineType Communication) UE or IoT device). In this case, the M-UE maycorrespond to a terminal mainly transmitting a low rate and requireshelp from a relay UE (R-UE). Or, the M-UE may correspond to a normal UE.In this case, the M-UE may correspond to a UE supporting D2Dcommunication for communication with an R-UE. Or, the M-UE maycorrespond to a UE capable of communicating with a cellular base stationwith the help of an R-UE, although the M-UE is unable to directlycommunicate with the cellular base station. Or, the M-UE may correspondto a type of a wearable terminal. A user is wearing a smart watch, neckband, or the like and information can be transmitted to a cellularnetwork via a cellular UE. The M-UE may have capability capable ofdirectly accessing a cellular base station. However, in order to performthe operation above, since considerable amount of repetitions or Txpower is required, battery of the M-UE can be quickly consumed. If theM-UE discovers an R-UE, the M-UE switches a mode to use the R-UE as arelay and can access a cellular network. The R-UE receives a signal froman M-UE and relays the signal to an eNB. Or, the R-UE receives a signalfrom the eNB and may be able to relay the signal to the M-UE. In somecases, the R-UE may perform an operation of forwarding a signal of theM-UE or a different UE. The R-UE may perform an operation of controllingtransmission or reception of the M-UE. Or, the R-UE may forward controlinformation of the M-UE to an eNB or a UE corresponding to a relayingtarget or the R-UE may correspond to a UE indicating atransmission/reception resource region of the M-UE.

In the following, various embodiments of the present invention relatedto transmission power control of M-UE and R-UE are explained.

M-UE Transmission Power Control (M-UE-to-R-UE Tx Power Control)

It may be able to use all or a part of S-RSRP (synchronization signalRSRP) or D-RSRP (Discovery signal RSRP) of an R-UE or DMRS (average)received power of SA or data for OLPC (open loop power control) of anM-UE. In particular, It may apply OLPC to M-UEs using all or a part ofS-RSRP of an R-UE, D-RSRP, and DMRS received power of SA or data.Specifically, it may be able to estimate PL (pathloss) using S-RSRPand/or D-RSRP and/or DMRS (average) received power of SA or data.According to the method above, since power control is performed on anR-UE, in the aspect of reception of the R-UE, the method has a merit inthat it is able to mitigate in-band emission or a near far problembetween M-UEs. In addition to the method above, it is able to utilizeRSRQ from the R-UE. In this case, when OLPC towards the R-UE is applied,either an eNB or the R-UE can configure P0, alpha value.

As a first method, an eNB configures P0 and alpha of an M-UE and OPLCparameters (P0, alpha) can be signaled via physical layer signaling orhigher layer signaling. In this case, since the eNB does not know achannel between the M-UE and an R-UE, the M-UE or the R-UE can reportsuch a measurement result as coverage, signal strength, received signalpower and the like between the M-UE and the R-UE to the eNB. The eNB cansignal P0 and alpha using a measurement result on a mutual channelmeasured by the M-UE or the R-UE. As a second method, the R-UE cansignal P0 and alpha values to be used by nearby M-UEs to the M-UE viaphysical layer signaling or higher layer signaling. The R-UE canidentify a channel state using all or a part of D-RSRP or S-RSRP of theM-UE and DMRS (average) received power of SA or data. Hence, the R-UEconfigures appropriate P0 and alpha values to enable the M-UE to applyOLPC. In some cases, if the R-UE configures the alpha by 0, the M-UE canconfigure fixed power.

The maximum transmit power of the M-UE can be determined by equation 1described in the following. According to the equation 1, when the M-UEdetermines max power, the max power can be restricted by OLPC of theeNB. And, it may be able to reduce in-band emission influence of asidelink reception UE by applying OLPC between sidelink UEs whileinterference towards an eNB is maintained by a certain level or below ina state that a power control value towards the eNB is set to an upperlimit value.

                                     Equation  12$P_{M - {UE}} = {\min \begin{Bmatrix}{P_{{CMAX},c},{{10\; {\log_{10}\left( M_{sidelink} \right)}} + P_{O\_ eNB} + {\alpha_{eNB} \cdot {PL}_{eNB}} + \Delta_{eNB}},} \\{{10\; {\log_{10}\left( M_{sidelink} \right)}} + P_{O\_ sidelink} + {\alpha_{sidelink} \cdot {PL}_{sidelink}} + \Delta_{sidelink}}\end{Bmatrix}}$

P_(CMAX,c) denotes maximum transmit power usable on a specific carrierc, M_(sidelink) denotes the number of RBs used for sidelinktransmission, P_(O_eNB) denotes initial (power offset) power valueconfigured by eNB, α_(eNB) denotes OLPC parameter alpha configured byeNB, PL_(eNB) denotes a pathloss between eNB and UE, Δ_(eNB) denotes apower offset value determined according to CLPC and/or MCS,P_(O_sidelink) denotes P-o (initial power) value configured betweensidelink UEs, α_(sidelink) denotes OLPC parameter between sidelink UEs,PL_(sidelink) denotes a PL value between sidelink UEs, and Δ_(sidelink)denotes a power offset value determined according to CLPC betweensidelink UEs and/or MCS. The P_(CMAX,c) can be replaced with maximumpower capable of being used as sidelink rather than maximum power on acarrier c.

R-UE Power Control (R-UE to M-UE, not Uu, DL Relaying)

All or a part of transmit power of the R-UE and a residual power valuecapable of being used for D2D (D2D power headroom) can be signaled tothe M-UE via physical layer signaling or higher layer signaling. Forexample, transmit power or a residual power value (e.g., power headroomor reserved power for sidelink transmission) of the R-UE can be signaledto M-UEs via a discovery signal of the R-UE. When the R-UE transmits asignal to the M-UE, if the M-UE fails to properly receive the signal,the method above can make a case of failing to receive a signal due to abad channel to be distinguished from a case of failing to receive asignal due to low transmit power. If the M-UE fails to receive a signaldue to the low transmit power, the R-UE is able to increase transmitpower via physical layer signaling or higher layer signal from the M-UE.The M-UE examines quality of a received signal and the transmit power ofthe R-UE. If it is necessary to more increase reception quality and theR-UE has remaining transmit power to be increased, the M-UE can ask theR-UE to increase the transmit power.

An OLPC (open loop power control parameter) (P0, alpha) used by the R-UEcan be signaled by a network via physical layer signaling or higherlayer signaling. In this case, the OLCP is applied to an eNB to mitigateinterference to a cellular channel. In this case, closed loop powercontrol can be controlled by the M-UE to make communication with theM-UE to be smoothly performed. In a broad sense, the maximum transmitpower of the R-UE can be controlled by the eNB and an upper limit of themaximum transmit power can be signaled by the eNB via physical layersignaling or higher layer signaling. In particular, the eNB can signalnot only P0, alpha but also the maximum upper limit and/or the maximumlower limit at a corresponding location to the R-UE. The R-UE candetermine transmit power upon the request of the M-UE or according toimplementation of the R-UE within a range permitted by the eNB.

The M-UE can ask the R-UE to increase or decrease transmit power viaphysical layer signaling or higher layer signal. The R-UE feeds backinformation on the request of the M-UE (increase/decrease of transmitpower, amount of the increase/decrease of transmit power, etc.) to anetwork and the network determines the final transmit power of the R-UE.According to the method above, it may be able to have a merit in thatthe network has all controllability and interference to the network canbe more actively controlled.

M-UE Transmission/Reception Resource Indication

The R-UE can indicate a resource position in which data and/or a controlsignal of the M-UE is transmitted via physical layer signaling or higherlayer signaling. In this case, although the R-UE can directly indicatethe resource position to an individual UE, the R-UE can indicate aresource region transmitted by nearby M-UEs. Hence, the M-UEs canautonomously select and transmit a resource in the resource region.Similarly, in order to perform a DL relay operation, R-UES can signal aresource position in which transmission is performed by the R-UEs orresource region information to the M-UE via physical layer signaling orhigher layer signaling.

As a different method, a transmission/reception resource of the M-UE canbe signaled by a network via physical layer signaling or higher layersignaling. In some cases, the M-UE can be positioned at the outside ofthe coverage of the network. In this case, the M-UE can performtransmission/reception in a predetermined resource region.

Discovery Operation and Capability of M-UE and R-UE

When the M-UE operates according to power control indicated by an eNBwhile the M-UE does not know information on whether or not the R-UEexists, if the R-UE appears in the vicinity of the M-UE, the M-UE mayoperate by changing the power control with power control heading towardsthe R-UE. In order to perform the operation above, it is necessary forthe M-UE and the R-UE to check the mutual existence. To this end, theM-UE and/or the R-UE are required to have capability capable oftransmitting and/or receiving a D2D discovery signal. In order to reduceUE complexity, the M-UE may have either capability capable oftransmitting a discovery signal or capability capable of receiving adiscovery signal. If the M-UE has capability capable of receiving adiscovery signal, the M-UE should perform an operation of receiving adiscovery signal in a manner of waking up in every certain period. Inthis case, if there are many R-UEs, the M-UE should have complexitycapable of decoding a plurality of discovery signals. Or, if the M-UEhas capability capable of transmitting a discovery signal only, the M-UEtransmits a discovery signal in a manner of waking up in every certainperiod. If the M-UE is able to handle sufficient complexity, the M-UEmay have capability capable of transmitting and receiving a discoverysignal.

In this case, in order to identify information on whether the R-UE hascapability capable of transmitting a discovery signal only or capabilitycapable of receiving a discovery signal only, it is necessary for theM-UE to transmit capability of the M-UE to the R-UE. For example, theM-UE can transmit the capability capable of transmitting/receiving adiscovery signal to the R-UE using a partial field of a MAC header or adiscovery message. On the other hand, the R-UE can also transmitcapability capable of transmitting/receiving a discovery signal via adiscovery message. If a counterpart UE has reception capability only (ifno discovery message is received), the R-UE stops reception and mayperform transmission only.

A power control operation of the M-UE can be changed according to adiscovery result. Specifically, if the M-UE and/or the R-UE check themutual existence (if a discovery signal of a counterpart UE issuccessfully decoded), a legacy power control parameter can beoverridden using power control required by the R-UE. Or, the M-UEmaintains power control towards the eNB for legacy uplink transmissiononly and can perform sidelink transmission using a power controlparameter towards the R-UE. In particular, a power control parameter forsidelink and a power control parameter for uplink can be separatelyconfigured. If the M-UE establishes a connection with the R-UE ordiscovers the R-UE, the M-UE stops performing uplink transmission andmay be then able to perform sidelink transmission (by applying powercontrol for sidelink).

Examples for the aforementioned proposed methods can also be included asone of implementation methods of the present invention. Hence, it isapparent that the examples are regarded as a sort of proposed schemes.The aforementioned proposed schemes can be independently implemented orcan be implemented in a combined (aggregated) form of a part of theproposed schemes. It may be able to configure an eNB to inform a UE ofinformation on whether to apply the proposed methods (information onrules of the proposed methods) via a predefined signal (e.g., physicallayer signal or upper layer signal).

Configurations of Devices for Embodiments of the Present Invention

FIG. 18 is a diagram for configurations of a transmitter and a receiver.

Referring to FIG. 18, a transmit point apparatus 10 may include areceive module 11, a transmit module 12, a processor 13, a memory 14,and a plurality of antennas 15. The antennas 15 represent the transmitpoint apparatus that supports MIMO transmission and reception. Thereceive module 11 may receive various signals, data and information froma UE on an uplink. The transmit module 12 may transmit various signals,data and information to a UE on a downlink. The processor 13 may controloverall operation of the transmit point apparatus 10. The processor 13of the transmit point apparatus 10 according to one embodiment of thepresent invention may perform processes necessary for the embodimentsdescribed above. The processor receives data from a first UE via areceive module, determines a subframe in which ACK/NACK is to betransmitted by comparing T-RPT (Time Resource Pattern for Transmission)of the first UE with T-RPT of a second UE, and can transmit ACK/NACK tothe first UE in the determined subframe in response to the receiveddata. Explanation on other details operations is replaced with theaforementioned contents.

Additionally, the processor 13 of the transmit point apparatus 10 mayfunction to operationally process information received by the transmitpoint apparatus 10 or information to be transmitted from the transmitpoint apparatus 10, and the memory 14, which may be replaced with anelement such as a buffer (not shown), may store the processedinformation for a predetermined time.

Referring to FIG. 18, a UE 20 may include a receive module 21, atransmit module 22, a processor 23, a memory 24, and a plurality ofantennas 25. The antennas 25 represent the UE that supports MIMOtransmission and reception. The receive module 21 may receive varioussignals, data and information from an eNB on a downlink. The transmitmodule 22 may transmit various signals, data and information to an eNBon an uplink. The processor 23 may control overall operation of the UE20.

The processor 23 of the UE 20 according to one embodiment of the presentinvention may perform processes necessary for the embodiments describedabove.

Additionally, the processor 23 of the UE 20 may function tooperationally process information received by the UE 20 or informationto be transmitted from the UE 20, and the memory 24, which may bereplaced with an element such as a buffer (not shown), may store theprocessed information for a predetermined time.

The configurations of the transmit point apparatus and the UE asdescribed above may be implemented such that the above-describedembodiments can be independently applied or two or more thereof can besimultaneously applied, and description of redundant parts is omittedfor clarity.

Description of the transmit point apparatus 10 in FIG. 18 may be equallyapplied to a relay as a downlink transmitter or an uplink receiver, anddescription of the UE 20 may be equally applied to a relay as a downlinkreceiver or an uplink transmitter.

The embodiments of the present invention may be implemented throughvarious means, for example, hardware, firmware, software, or acombination thereof.

When implemented as hardware, a method according to embodiments of thepresent invention may be embodied as one or more application specificintegrated circuits (ASICs), one or more digital signal processors(DSPs), one or more digital signal processing devices (DSPDs), one ormore programmable logic devices (PLDs), one or more field programmablegate arrays (FPGAs), a processor, a controller, a microcontroller, amicroprocessor, etc.

When implemented as firmware or software, a method according toembodiments of the present invention may be embodied as a module, aprocedure, or a function that performs the functions or operationsdescribed above. Software code may be stored in a memory unit andexecuted by a processor. The memory unit is located at the interior orexterior of the processor and may transmit and receive data to and fromthe processor via various known means.

Preferred embodiments of the present invention have been described indetail above to allow those skilled in the art to implement and practicethe present invention. Although the preferred embodiments of the presentinvention have been described above, those skilled in the art willappreciate that various modifications and variations can be made in thepresent invention without departing from the spirit or scope of theinvention. For example, those skilled in the art may use a combinationof elements set forth in the above-described embodiments. Thus, thepresent invention is not intended to be limited to the embodimentsdescribed herein, but is intended to accord with the widest scopecorresponding to the principles and novel features disclosed herein.

The present invention may be carried out in other specific ways thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein. The present invention is not intendedto be limited to the embodiments described herein, but is intended toaccord with the widest scope consistent with the principles and novelfeatures disclosed herein. In addition, claims that are not explicitlycited in each other in the appended claims may be presented incombination as an embodiment of the present invention or included as anew claim by subsequent amendment after the application is filed.

The embodiments of the present invention can be applied to variousmobile communication systems.

What is claimed is:
 1. A method of performing device-to-device (D2D) communication by a user equipment (UE) in a wireless communication system, the method comprising: determining i) a first power value based on a downlink pathloss between a network and the UE and ii) a second power value based on a sidelink pathloss between the UE and a counterpart UE of the D2D communication; determining a transmission power for the D2D communication based on a minimum value among the first power value and the second power value; and performing the D2D communication to the counterpart UE based on the transmission power.
 2. The method according to claim 1, wherein the UE is configured by the network with i) a first parameter for a first power control based on the downlink pathloss and ii) a second parameter for a second power control based on the sidelink pathloss, wherein the first power value is determined based on the first parameter and the downlink pathloss, and the second power value is determined based on the second parameter and the sidelink pathloss.
 3. The method according to claim 2, wherein the first parameter comprises a first power offset configured by the network, and the second parameter comprises a second power offset configured by the network.
 4. The method according to claim 2, wherein the first parameter comprises a first alpha value to be multiplied with the downlink pathloss, and the second parameter comprises a second alpha value to be multiplied with the sidelink pathloss.
 5. A user equipment (UE) in a wireless communication system, the UE comprising: at least one transceiver; at least one processor; and at least one computer memory operably connectable to the at least one processor and storing instructions that, when executed, cause the at least one processor to perform operations comprising: determining i) a first power value based on a downlink pathloss between a network and the UE and ii) a second power value based on a sidelink pathloss between the UE and a counterpart UE of a device-to-device (D2D) communication; determining a transmission power for the D2D communication based on a minimum value among the first power value and the second power value; and performing the D2D communication to the counterpart UE based on the transmission power.
 6. The UE according to claim 5, wherein the UE is configured by the network with i) a first parameter for a first power control based on the downlink pathloss and ii) a second parameter for a second power control based on the sidelink pathloss, wherein the first power value is determined based on the first parameter and the downlink pathloss, and the second power value is determined based on the second parameter and the sidelink pathloss.
 7. The UE according to claim 6, wherein the first parameter comprises a first power offset configured by the network, and the second parameter comprises a second power offset configured by the network.
 8. The UE according to claim 6, wherein the first parameter comprises a first alpha value to be multiplied with the downlink pathloss, and the second parameter comprises a second alpha value to be multiplied with the sidelink pathloss.
 9. An apparatus for a user equipment (UE), the apparatus comprising: at least one processor; and at least one computer memory operably connectable to the at least one processor and storing instructions that, when executed, cause the at least one processor to perform operations comprising: determining i) a first power value based on a downlink pathloss between a network and the UE and ii) a second power value based on a sidelink pathloss between the UE and a counterpart UE of a device-to-device (D2D) communication; determining a transmission power for the D2D communication based on a minimum value among the first power value and the second power value; and performing the D2D communication to the counterpart UE based on the transmission power.
 10. A computer readable storage medium storing at least one computer program comprising instructions that, when executed by at least one processor, cause the at least one processor to perform operations for a user equipment (UE), the operations comprising: determining i) a first power value based on a downlink pathloss between a network and the UE and ii) a second power value based on a sidelink pathloss between the UE and a counterpart UE of a device-to-device (D2D) communication; determining a transmission power for the D2D communication based on a minimum value among the first power value and the second power value; and performing the D2D communication to the counterpart UE based on the transmission power. 